The epithelial to mesenchymal transition (EMT) is a program of events characterized by loss of cell polarity, enhanced cell motility, and increased cell invasion. While this process is essential for normal embryonic development, its deregulation in the adult promotes metastasis. The broad, long term objectives of this proposal are to understand how the epithelial to mesenchymal transition initiates the loss of cellular polarity and how this depolarization might contribute to cancer progression. The central hypothesis is that the transcriptional represser Snail, a key regulator of the EMT, affects the apico-basal polarity complexes Crumbs3-PALS1-PATJ and Par6-Par3-aPKC and that loss of these polarity complexes enhances cancer progression. This hypothesis is based on the long-appreciated observation that the epithelium appears depolarized in many carcinomas, and on data from model organisms demonstrating that loss of proper epithelial architecture results in profound hyperproliferation. Previous work from this laboratory and others has revealed that the Crumbs and Par6 polarity complexes are required for the formation of the tight junction and maintenance of cell polarity. Based on these observations, the experimental focus of this proposal is on the novel Crumbs and Par6 epithelial polarity complexes during EMT. The specific aims are to: (1) Elucidate the specific defects in apico-basal polarity complexes induced by Snail expression in epithelial cells. The study will examine how Snail affects the localization and protein levels of the polarity complexes, if it reduces the expression of the tight junction component genes, if E-cadherin expression can rescue the polarization defects, and if elevated levels of Snail correlate with the suppression of E-cadherin and CrumbsS in human tumor samples. (2) Analyze the biological effects of Snail-induced depolarization in epithelial cells and evaluate whether selective re- expression of CrumbsS modulates proper biological function. The study will investigate if Snail disrupts other cellular processes closely associated with cell polarity such as mitotic spindle pole alignment and cell migration, if re-expression of CrumbsS reverses any functionally altered phenotypes, and whether the specific loss of CrumbsS modulates cancer cell growth or migration. Biochemical, genetic, proteomic, and microscopy-based methods will be used to address these aims. The relevance of this project to public health is that it will further our understanding of the precise molecular mechanisms resulting in cancer cell migration, invasion, and metastasis and potentially identify new targets for cancer therapy. [unreadable] [unreadable] [unreadable]